Preventing formation of color fog in emulsions



Patented Oct. 10, 1944 PREVENTING FORMATION OF COLOR FOG IN EMULSIONSPaul W. Vittum and N. Y., assignors to Lot S. Wilder, Rochester, EastmanKodak Company,

Rochester, N. Y., a corporation of New Jersey No Drawing. ApplicationJuly 31, 1941, Serial No. 404,894

13 Claims.

This invention relates to color photography and particularly to a methodfor preventing the formation of color fog in photographic emulsions.

The incorporation of color forming components in silver halide emulsionlayers was described by Fischer in U. S. Patent 1,102,028, granted June30, 1914. These components are compounds such as phenolic hydroxylcompounds or compounds with reactive methylene groups, which are capableof reacting with the development product of aromatic amino photographicdevelopers to produce dyes. The color formers may be added directly tothe emulsion layers as described by Fisher or they may be incorporatedin a separate medium which is insoluble in the carrier for the sensitivesilver halide as described in Mannes and Godowsky U. S. Patent2,304,940, granted December 15, 1942, and Jelley and Vittum U. S. PatentNo. 2,322,027, granted June 15,1943.

A difficulty frequently encountered in these processes is the formationof color fog or stain. With materials in which color forming compoundsare incorporated in the sensitive layer, dye fog is formed along withthe customary silver fog met in black and white photography but inaddition fog is also formed from any oxidized developer formed by theaction of air, oxidizing silver removal baths, etc. It is well knownthat in these processes the dye is formed when the silver halide isreduced to metallic silver, thereby oxidizing the developing agent to aform which couples with the color former. Once the developing agent isoxidized, it couples immediately with the color former whether aphotographic imageis present or not. Aerial oxidation of the developeror oxidation by means other than the photographic image, therefore,converts the developer to a form Which will immediately react with thecolor former to produce a color fog or stain. Fog or stain arising fromthese causes is not readily controlled by the same procedures used toreduce or control silver fog.

It is, therefore, an object of the present invention to provide a meansfor reducing or eliminating the formation of color fog inincorporated-coupler photographic emulsions. A further object is toprovide a color forming photographic emulsion having non-diffusingcouplers incorporated therein, which is less subject to the formation ofcolor fog. Other objects will appear from the following description ofour invention.

These objects are accomplished by incorporating in a photographicemulsion containing nondifiusing color formers, a non-coupling organicring compound having one or more hydroxyl substituents and functioningas a reducing agent. Our method is intended for use with emulsions whichproduce a negative image on development. whether they are used fordirect exposure to a subject, or as a printing material for a negativeor positive. Such materials may obviously be used to produce an imageproduce a positive image directly except after exposure to a negative.In the case of colorforming development, a colored negative image mightbe formed by direct development, or by reversal.

We have found that color fog or stain in incorporated coupler materialsmay be appreciably reduced by adding to the emulsion layers beforecoating or after coating and before processing a substance or substanceshaving reducing properties as described above. It is believed that thesesubstances exert an anti-oxidant action either by preventing theformation of extraneous oxidized developer or by reducing any extraneousoxidized developer before it has an opportunity to react with a colorformer. Whatever the mechanism of the reaction, we have found itpossible in many cases to reduce markedly the fog or stain densitywithout seriously damaging the densities of the dye developed images.

Compounds suitable for use according to our invention are hydroquinoneand certain of its derivatives such'as amyl hydroquinone, laurylhydroquinone, heptyl hydroquinone, diamyl hydroquinone, and dioctylhydroquinone. Other non-coupling organic carbon ring compoundscontaining at least one hydroxyl substituent which may be used are thefollowing compounds:

CH3 H, cm (3H3 on. CH3 J-(CH2)aCH(CH OH(CHmCHCHa a-Tocopherol CnHzsDodecyl catechol The reducing agents used according to our invention maybe incorporated in single layer coatby reversal, but not to ings or inone or more layers of a multi-layer coating. It may be desirable, forexample, to have the reducing agent present in only one or two layers ofa multi-layer coating and in this case a substance would be used whichdoes not wander freely in gelatin such as lauryl hydroquinone or dioctylhydroquinone. In cases where the reducing agent was desired to beuniformly distributed throughout the whole film, one might use compoundsof lower molecular weight such as hydroquinone or its simplesubstitution products.

When the reducing agent is used with emulsions containing a couplerdissolved in agents insoluble in gelatin as in the processes describedin Mannes and Godowsky Patent 2,304,940 and Jelley and Vittum Patent No.2,322,027 it may be added either to the emulsion itself or to thecouplercarrier along with the coupler.

In general, the reducing agents are used in quantities ranging from 0.1gram to 1.0 gram per liter of gelatino silver halide emulsion. Thesevalues are, however, only illustrative. As a specific example of theincorporation of a reducing agent into a silver halide emulsioncontaining coupler, the following is suitable: To 50 cc. of greensensitized silver bromide emulsion containing 0.25 gram of magentacoupler, 1-phenyl-3- pentadecyl-S-pyrazolone, there was added, beforecoating, 0.02 gram of diamyl hydroquinone.

Where it is desired to introduce the reducing agent after coating andbefore processing, the sensitive material may be bathed inan aqueoussolution of the reducing agent such as the following pre-bath:

Hydroquinone grams 0.2 Potassium bromide do 2.0 Sodium sulfite do 2.0Water to cc.. 1000 The reducing agent may be added to one of the filmprocessing baths such as a prebath or the first developer bath. In thecase of negative development as disclosed, for example, in Jelley andVittum U. S. Patent 2,322,027, the first developer is a color-formingdeveloper. The reducing agent may, therefore, be used in a colorformingdeveloper such as a diethyl-p-phenylenediamine developer. Our method isintended for use principally with emulsions which produce a negativeimage upon direct development, that is, emulsions in which a negativeimage would be formed upon development after exposure under apositive'image or in which positive images would be formed on directdevelopment after exposure under a negative image. It may also be usedfor reversal color development.

Our process is particularly useful with paper materials, where it isespecially important to reduce the minimum (fog) densities. This appliesboth to negative-developed paper and to reversal paper and transparencymaterials.

It will be understood that the examples and modifications disclosedherein are by way of example only and that our invention is to be takenas limited only claims.

We claim:

1. A color forming photographic emulsion which produces a negative imageon development, comprising a non-difiusing coupler incorporated thereinand as an inhibitor of color fog a hydroquinone having a carbon chain ofat least five carbon atoms.

2. A color forming photographic emulsion by the scope of the appendedwhich produces a negative image on development, comprising anon-diffusing coupler incorporated therein and as an inhibitor of colorfog an amyl hydroquinone.

3. A color-forming photographic emulsion which produces a negative imageon development, comprising a non-difiusing coupler incorporated thereinand as an inhibitor of color fog amyl hydroquinone.

4. A color-forming photographic emulsion which produces a negative imageon development, comprising a non-diifusing coupler incorporated thereinand as an inhibitor of color fog lauryl hydroquinone.

5. The method of preventing the formation of color fog in a photographicsilver halide emulsion which produces a negative image on developmentand which contains a non-diifusing coupler there-. in, comprisingexposing said emulsion and developing it with a primary aromatic aminodeveloping agent in the presence of a non-coupling hydroxy benzene.

6. The method of preventing the formation of color fog in a photographicemulsion which produces a negative image on development and whichcontains a non-diifusing coupler therein, comprising incorporating insaid emulsion as an inhibitor of color fog a non-coupling hydroxybenzene, exposing with a primary aromatic amino developing agent.

7. The method of preventing the formation of color fog in a photographicemulsion which produces a negative image on development and whichcontains a non-diffusing coupler therein, comprising incorporating insaid emulsion as an inhibitor of color fog a non-coupling hydroxybenzene and a carbon chain of at least five carbon atoms, exposing saidemulsion and developing it with a primary aromatic amino developingagent.

8. The method of preventing the formation of color fog in a photographicemulsion which produces a negative image on development and whichcontains a non-difiusing coupler therein, comprising incorporating insaid emulsion as an inhibitor of color fog a hydroquinone having acarbon chain of at least five carbon atoms.

9. The method of preventing the formation of color fog in a photographicemulsion which produces a negative image on development and whichcontains a non-diffusing coupler therein, comprising incorporating insaid emulsion as an inhibitor of color fog amyl hydroquinone.

10. The method of preventing the formation of color fog in aphotographic emulsion which produces a negative image on development andwhich contains a non-diffusing coupler therein, comprising incorporatingin said emulsion as an inhibitor of color fog lauryl hydroquinone.

11. The method of preventing the formation of color fog in aphotographic emulsion which produces a negative image on develpment andwhich contains a non-diffusing coupler therein, comprising bathing saidemulsion after exposure and before development in a solution of anon-coupling hydroxy benzene, and incapable of develop: ing a visibleimage therein, and then developing said emulsion with a primary aromaticamino developing agent.

12. The method of preventing the formation of color fog in aphotographic emulsion which produces a negative image on development andwhich contains a non-difiusing coupler therein, comprising bathing saidemulsion after exposure and before development in a solution ofhydroquinone incapable of developing a visible image therein saidemulsion and developing it aoeaaoo n;

and then developing said emulsion with a primary aromatic aminodeveloping agent.

13. The method of preventing the formation of color fog in aphotographic emulsion which produces a negative image on developmentand. which contains a non-diffusing coupler therein, comprising bathingsaid emulsion after exposure and before development in a solutioncontaining about 0.2 gram per liter of hyciroquinone, and thendeveloping said emulsion with a primary aromatic amino developing agent.

PAUL W. VITITUIVI. LQT S. WILDER.

